Call to tackle needle grass early

A weed inflicting “excruciating” pain on Canterbury livestock has scientists estimating it could cost the country more than $1 billion if allowed to spread nationwide.

Chilean needle grass (Nassella neesiana) is known to have taken hold in Hawke’s Bay, Marlborough and Canterbury.

Sharp penetrating seeds can blind livestock and painfully pierce their pelt and carcass. The loss of pasture quality and grazing access from this results in farm production taking a financial hit.

AgResearch has run the calculator over potential losses if nothing was done to stop it spreading through most of New Zealand.

New research estimates the loss to the pastoral sector would be $192million if the weed took about 200 years to reach 90% occupation of its potential climatically suitable range, which covers nearly 4,000,000ha. This would rise to $1.16b if the weed’s spread rate took 100 years.

Scientists calculate these losses justify spending $5.3m a year to prevent its spread for the longer scenario, and $34m for the shorter one.

Chilean needle grass one of about 22,000 species of introduced plants in New Zealand.

The weed is found in about 2500ha in Marlborough and 200ha in Hawke’s Bay, and is thought to have infested about 330ha of Canterbury properties.

AgResearch principal scientist Dr Graeme Bourdot said needle grass was first found in a North Canterbury vineyard and pastures in November 2018, and was difficult to contain.

“Subsequently it was found in several other nearby locations in that part of North Canterbury. It sort of inhabits the same dryland, north-facing country as nassella tussock, but it’s able to get into the damper, more competitive areas and its equally as drought tolerant.

“You can’t remove it selectively with the synthetic herbicides and there’s no bio-control agent for it at the moment.

“So the only thing a farmer can do if it gets in a paddock is hold stock from grazing that paddock during the seeding period — from late November to February — to avoid the serious animal welfare issues and minimise spreading it.”

He said the sharp seeds had a hydroscopic awn, acting like a ratchet in a drill, to twist into wool, with backwards pointing bristles keeping it from falling out.

“Eventually they go into the skin and either lodge into the skin or go right through into the underlying muscles and that results in, I would imagine, some excruciating pain for the animal.

“Those carcasses would need to be downgraded and the skins are worthless, because they’re full of holes and many animals will be blinded by the seeds because they go into their eyes.”

He said there were other nasty grasses for livestock, but none of them had the same pronounced drilling mechanism, and removing seeds from sheep would be virtually impossible.

Removing animals from a paddock resulted in reduced revenue, he said.

“Needle grass occupies less than 0.1% of its potential range and currently our models show that under the current climate there’s 4,000,000ha of of climatically suitable sheep and beef pasture land where the seed could grow.

“Under future climates that potential distribution could be closer to 6,500,000ha and currently in Marlborough, Hawke’s Bay and Canterbury there’s a little over 3000ha, so we have an opportunity to stop this slow-spreading weed from spreading all over the other susceptible regions.”

Dr Bourdot said researchers had worked with Manaaki Whenua-Landcare Research to analyse management scenarios for “sleeper” weeds.

They were now working with regional councils, Doc and the Ministry of Primary Industries to develop a web-based tool for making decisions about investing in management programmes.

“The exciting part is that we now have the ability through our research to develop models and tools to identify sleeper weeds, predict how and where they will spread in a changing climate, and estimate the economic and environmental damage that would result.”

He said Australian scientists had confirmed it was possible to stop the weed’s spread with sufficient will and resources.

“Our analysis really supports the idea that it’s a national problem, and we should be treating it as a national problem and having a nationally co-ordinated programme to manage its spread.”

Councils were keen to work together nationally, he said.

AgResearch senior scientist Chris Buddenhagen said a nationally co-ordinated approach would include surveillance in susceptible regions and control measures in the infested regions.

Auckland Council biosecurity principal adviser Imogen Bassett said Auckland and other councils were working hard to prevent the grass’ spread, and the new research highlighted the importance of this work.

“We know it is much more cost-effective for us to act early, to prevent future weed invasions than to deal with them once they become widespread,” she said.

She said councils relied on good information to help them prioritise the many potential weeds.


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